Choline is an essential nutrient for humans which has important key functions in the body, e.g. precursor for acetylcholine or phospholipids. Further it is a quaternary ammonium cation of biological origin. However, the most important characteristic is its bulky, unsymmetrical structure. Therefore, in this thesis it is shown as a very efficient counterion to lower the Krafft temperature of surfactants and the melting or freezing point of ionic liquids and deep eutectic solvents. These substances were investigated for eventual applications as extracting agent, in formulations or for washing processes. For this purposes a low cytotoxicity is important. It was confirmed by performing MTT-assays of these substances with HeLa and SK-MEL-28 cells.
The first part of this thesis is focused on the synthesis of choline carboxylate based ionic liquids. The design of the ionic liquids is divided into two approaches. Firstly, the melting point could be further lowered, beside the use of a bulky, unsymmetrical cation, by decreasing the chain length of the carboxylate anion (ChCm with m = 2, 4, 6, 8, 10) and secondly, by inserting a double bond into the alkyl chain (choline oleate). Therefore, choline carboxylates ChCm with chain lengths of m = 2, 4, 6, 8 and 10 and choline oleate were synthesized and the focus is set on the physico-chemical characterization and the investigation of the influence of the alkyl chain length and the double bond in the alkyl chain on the aqueous phase behavior and the temperature dependent behavior of the neat choline carboxylates. Several experimental techniques like wide and small angle X-ray scattering, polarizing optical microscopy, NMR spectroscopy and differential scanning calorimetry were used for the characterization.
The second main part of this thesis is focused on the investigation of new promising, biocompatible and biodegradable surfactants for a possible application as laundry detergents. From other studies it is known that choline dodecylsulfate is a less salt sensitive surfactant and possesses a more acidic headgroup compared to the choline carboxylates and its Krafft temperature is lower compared to the one of sodium dodecylsulfate. A better washability at low temperatures is normally obtained by increasing the chain length, while the Krafft temperature of the surfactant remains below room temperature. Thus, choline hexadecylsulfate was synthesized as a better washing surfactant. The temperature dependent binary phase diagrams of choline dodecylsulfate and choline hexadecylsulfate with water were investigated with small angle X-ray scattering, polarizing optical microscopy and visual observations and compared to the binary phase diagrams of the sodium analogs and to choline carboxylates. In addition, the thermotropic phase behavior was studied and compared to the one of choline carboxylates ChCm with m = 8, 10 and oleate. Last but not least, the washability of choline alkylsulfate surfactants and mixtures of choline alkylsulfates with different chain length or with a common laundry detergent was evaluated with the help of washing, foamability and foam stability tests. Furthermore, the oil solubilization capacity of the pure surfactants was evaluated. These tests show a better washing ability for mixtures of choline alkylsulfates with different chain length or of choline hexadecylsulfate with a common laundry detergent compared to the single surfactants.
As third part of the thesis a strategy to design room temperature liquid and fully dissociated deep eutectic solvents composed of choline bicarboxylate and choline chloride (and urea) was introduced. Therefore at room temperature liquid and fully dissociated choline glutarate based deep eutectic solvents were synthesized. The mixtures were characterized according to their solvent properties with density, viscosity and conductivity measurements
